ABSTRACT
Indoor air quality (IAQ) is a significant concern that affects our health. Recent studies show how poor IAQ amplifies the effects of airborne viruses, which endanger the health of the population relative to the COVID-19. This study aims to find the relationship among IAQ, the location of the air outlet valve and the behavior of the IAQ indicators in the cardiac care unit (CCU) at Namazi Hospital, Shiraz, Iran. In this context, the condition of the air outlet valve can play an important part in preparing a better IAQ. To test the hypothesis, articles based on IAQ guidelines have been studied. Also, certain emissions (CO2, CO, PM2.5 and PM10) have been measured, and the relationship between IAQ, the location of the air outlet valve and the behavior of these emissions in the patient's room at Namazi Hospital. This room has been analyzed using computational fluid dynamics for the prediction of the specification of incoming air flow particles. Also, a Eulerian–Lagrangian model was used. In constant, the turbulence model (realizable k–ԑ) and discrete particle model were employed. The results show that when the outlet valve is placed on the wall at 20 cm, it decreased particle deposition in the room, and as a result, IAQ will be improved and at the same time, the chances of transmitting infectious diseases will be reduced. It is also indicated that a higher amount of particle deposition fraction (ca. 0.71) obtains when the outlet valve is located on the top of the wall. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
ABSTRACT
Ventilation in confined spaces is essential to reduce the airborne transmission of viruses responsible for respiratory diseases such as COVID-19. Mechanical ventilation using purifiers is an interesting solution for elevator cabins to reduce the risk of infection and improve the air quality. In this work, the optimal position and blowing direction of these devices to maximize ventilation and minimize the residence time of the air inside two cabins (large and small) is studied. Special attention is devoted to idle periods when the cabin is not used by the passengers, in order to keep the cabin ambient safe and clean, avoiding that the trapped air in the cabin (after its use) could suppose a reservoir for contaminants. CFD numerical models of two typical cabin geometries, including the discretization of small slots and grilles for infiltration, have been developed. A full 3D URANS approach with a k-epsilon RNG turbulence model and a non-reactive scalar to compute the mean age of air (MAA) was employed. The CFD results have been also validated with experimental measurements from a home-made 1:4 small-scale mock-up. The optimal position of the purifier is on the larger sidewall of the cabins for a downward blowing direction (case 1 of the database). Flow rates in the range of 0.4–0.6 m3/min, depending on the size of the cabin, are sufficient to assure a correct ventilation. Upward blowing may be preferable only if interaction of the jet core with the ceiling or other flow deflecting elements are found. In general, the contribution of infiltrations (reaching values of up to 10%), and how these secondary flows interact with the main flow pattern driven by the purifier, is relevant and not considered previously in the literature. Though an optimal position can improve ventilation considerably, it has been proven that a good choice of the purification flow rate is more critical to ensure an adequate air renewal. © 2022 The Authors
ABSTRACT
The purpose of a ventilation system for indoor spaces is to create a safe environment for the occupants by diluting the concentration levels of hazardous contaminants and to minimize the risk of infection due to spread of airborne pathogens. The effectiveness of ventilation system depends on several inter related factors including the supply airflow rate, number and locations of supply diffusers, and number and locations of return grilles. With the help of Computational Fluid Dynamics (CFD) analyses, this study systematically evaluates the impact of three different HVAC configurations on the airflow patterns, distribution of contaminant, and the risk of infection in a small office space with two cubicles. The HVAC configuration with a single supply and a single return can create adverse airflow patterns which can promote spread of contaminants and increase the risk of infection farther from the source. When an additional supply diffuser is introduced with the same single return, the zone of high risk of infection remained in the vicinity of the source. However, the overall risk of infection in the space remained the same. Addition of another return created aerodynamic containment zones in the space which provided easy path for the contaminated air to leave the space and reduced the overall risk of infection. Since the location of an infected individual is not known a priori, the aerodynamic containment with distributed supply and distributed return can be the best strategy for reducing the probability of infection in indoor spaces. These studies demonstrate that CFD analyses can help in identifying the potential risk of high infection due to poor airflow distribution into a space and can provide valuable insights for developing appropriate mitigation strategies to create safe indoor environment.
ABSTRACT
The wavelength band of200-280 nm of UV-C radiation generated by the Ultraviolet Germicidal Irradiation (UVGI) system can destroy the reproduction ability of microorganisms. Severalfactors related to UVfixtures, HVAC layout, and the resulting airflow flow patterns can affect the performance of upper-room UVGI applications. With the help of Computational Fluid Dynamics (CFD) analyses, this study systematically evaluates the impact of UV-C intensities on the effectiveness of an upper room UVGI system. It shows that the addition of even a small amount of UV-C energy in the upper region of space can significantly reduce the probability of infection as predicted by the Wells-Riley model. Increasing the UV-C output shows a further reduction in the infection probability, although with a diminishing impact. A further investigation is necessary to evaluate the effect of airflow patterns on the performance of UVGI systems. These studies demonstrate that CFD analyses can help optimize the performance of UVGI systems to minimize the probability of infection in indoor spaces.
ABSTRACT
An aerodynamic optimization for a Droop-Nose Leading-Edge (DNLE) morphing of a well-known UAV, the UAS-S45, is proposed, using a novel Black Widow Optimization (BWO) algorithm. This approach integrates the optimization algorithm with a modified Class-Shape Transformation (CST) parameterization method to enhance aerodynamic performance by minimizing drag and maximizing aerodynamic endurance at the cruise flight condition. The CST parameterization technique is used to parameterize the reference airfoil by introducing local shape changes and provide skin flexibility to obtain various optimized morphing airfoil configurations. The optimization framework uses an in-house MATLAB algorithm, while the aerodynamic calculations use the XFoil solver with flow transition estimation criteria. These results are validated with a CFD solver utilizing the Transition (γ−Reθ) Shear Stress Transport (SST) turbulence model. Numerical studies verified the effectiveness of the optimization strategy, and the optimized airfoils have shown a significant improvement in overall aerodynamic performance by up to 12.18% drag reduction compared to the reference airfoil, and an increase in aerodynamic endurance of up to 10% for the UAS-S45 optimized airfoil configurations over its reference airfoil. These results indicate the importance of leading-edge morphing in enhancing the aerodynamic efficiency of the UAS-S45 airfoil.
ABSTRACT
Creating a good local microclimate can alleviate urban heat islands and poor urban ventilation. During the COVID-19 epidemic, citizens' cross-city and cross-regional activities were restricted, and most activities were conducted in open/semi-open areas next to residential areas, and local pedestrians were also quantitatively explored. The new characteristics of the microclimate bring difficulties. The RNG k-ε model in the Reynolds time-average method is used to simulate and analyze the wind environment of a typical street valley with a pocket park in a hot summer and a cold winter, and explore whether there are plants in the pocket park. The results show that the results obtained by the used turbulence model, initial edge conditions and numerical method are in good agreement with the selected verification experimental results, which meet the needs of the wind environment simulation of the pocket park. Only under the action of the pocket park, the pedestrian area is dimensionless. The difference in wind speed can reach 0.5 compared to the time when there is no park. When the plants in the park are added, the average wind speed in the pedestrian area of the surrounding street valley is less affected by the plants, and the dimensionless wind speed is only reduced by 0.1 in the core area of the park. Pocket parks can significantly improve the low wind speed in pedestrian areas, and the research results can provide reference for the design of low-carbon livable blocks and microclimate simulation during the epidemic period.